Commercially, polybutadiene, polyisoprene, and copolymers of butadiene and isoprene have been prepared from solution or bulk polymerization processes using a transition metal catalyst such as those having a precursor component of a nickel or cobalt compound or using a rare earth metal catalyst such as those having a precursor component of a neodymium compound. In solution or bulk polymerizations using almost any cobalt or nickel transition metal catalyst or any neodymium rare earth metal catalyst, the polymers produced have commercial range molecular weights (MW), and narrow molecular weight distributions (MWD). In these bulk and solution polymerization procedures, shorter residence time, chain transfer agent addition, and/or higher reaction temperature are used to control MW and/or MWD. Due to process limitations in the solution system the ranges of polymer molecular weight and MWD are restricted. The commercial polymers produced in solution and slurry processes are produced from the reactor in bale-like form and require additonal pulverization steps.
Only recently, it has been discovered that polybutadiene and polyisoprene can be prepared in the gas phase, particularly in the gas phase fluidized bed reactor. See U.S. Pat. Nos. 4,994,534; 5,453,471; and also WO 96/04322; and WO 96/04323. Unfortunately, many of the catalysts employed in solution/bulk polymerizations, when used in fluidized reactors, particularly gas phase fluidized reactors, produce polymers having low MW, and narrow MWD.
Accordingly, there is an ongoing need to be able to utilize these catalysts in fluidized polymerization processes to produce polymers (e.g., polybutadiene, polyisoprene, and copolymers of butadiene and isoprene) having any desired molecular weights and MWD, especially molecular weights and MWD equivalent to commercially available polymers produced by solution/bulk polymerizations processes. In addition, there is a need to utilize these same catalysts in gas phase polymerizations to produce polymers with much higher molecular weights and broad or bimodal MWD. This is believed to be necessary because it is thought that by increasing the MWD of the polymer, subsequent end-use processing would become easier (see EP 754,705-A2 and an article by E. Lauretti, B. Miani, and F. Mistrali in Tire Technology International, 1993, pp. 72-78).